Paving block formed of rubber crumb and a method of manufacturing the same

ABSTRACT

A hollow paving block comprises a substantially planar member having a first surface and a second surface opposite the first surface. The first surface of the planar member is a textured surface which functions as a top of the paving block. A side wall extends along and away from a periphery of the second surface of the planar member to define a cavity in the paving block. The side wall has a bevelled edge which extends about a mouth of the cavity. At least one protrusion extends along the second surface of the planar member. The paving block is formed in part from crumb rubber and polyolefin.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of provisional application61/367,342 filed in the United States Patent and Trademark Office onJul. 23, 2010, the disclosure of which is incorporated herein byreference and priority to which is claimed.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to paving blocks and, in particular to apaving block formed in part from rubber crumb and a method ofmanufacturing the same.

2. Description of the Related Art

Millions of tires are discarded every year in the United States. TheUnited States Environmental Protection Agency estimated that in 2003alone approximately 290 million tires were discarded in the UnitedStates. It is not desirable to send the discarded tires to landfillsbecause large volumes of tires can rapidly fill the limited spaceavailable at the landfills. There is accordingly an ongoing need reducethe number of used tires sent to landfills. One solution is to processthe discarded tires to produce crumb rubber which are granules ofvulcanized tire rubber with the steel and fibre removed.

It is known to produce crumb rubber through mechanical stepwise grindingor a cryogenic freezing process. In the mechanical process, tires areshredded or cut into smaller pieces which are put through granulators toseparate and remove loose steel and fibre. The remaining vulcanizedrubber granules are ground in a cracker mill to produce crumb rubber ofa desired mesh size. In the cryogenic process, tires are shredded or cutinto smaller pieces which are frozen in liquid nitrogen as they passthrough a cryogenic tunnel. The frozen tire pieces then pass through aseries of cracker mills where they are shattered into their threecomponent parts, namely, rubber, steel and fabric. The cryogenic processis generally more expensive but produces smoother and smaller granulesof crumb rubber.

The primary use of crumb rubber is in rubberized asphalt which is apaving material comprised of asphalt concrete mixed with rubber crumb.However, crumb rubber may be used in other applications includingpathways, ground cover under playground equipment, resilient flooring inrecreational facilities, running tracks, and synthetic turf fields.Crumb rubber has also been used in modular paving blocks.

U.S. Pat. No. 6,602,586 issued on Aug. 5, 2003 to Kakimoto et al.discloses a paving block designed to be paved on an underlying base toabsorb impacts. The block includes rubber chips mixed with a resinbinder to form a powdery rubber-containing layer which integrallyoverlays a vulcanized rubber base. The powdery rubber-containing layerfunctions to absorb impacts and the rubber chips preferably includecrumb rubber.

U.S. Pat. No. 7,344,334 issued on Mar. 15, 2008 to Thorkelson disclosesa paver system including at least one substrate and a plurality ofpaving blocks. Each of the paving blocks has a bottom surface configuredto engage a top surface of the substrate, thereby preventing lateralmovement of the paving blocks. The paving blocks and substrate may beformed from 20 to 80 mesh rubber crumb and a plastic which acts as abinder and forms a matrix for the crumb rubber.

United States Patent Application Publication Number 2009/0297267published on Dec. 3, 2009 to Glynn discloses a paving block formed of atleast crumb rubber and binder. The paving block is a cast block which ispreferably formed by hot melt molding or hot pressure molding. Eachblock has at least one protruding male connector and one recessed femaleconnector. The female connector is configured to receive a maleconnector of a similar block, thereby allowing adjacent paving blocks tobe connected.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an improved pavingblock formed in part from rubber crumb.

It is another object to provide an improved method of manufacturing apaving block formed in part from rubber crumb.

There is accordingly provided a hollow paving block comprising asubstantially planar member having a first surface and a second surfaceopposite the first surface. The first surface of the planar member is atextured surface which functions as a top of the paving block. A sidewall extends along and away from a periphery of the second surface ofthe planar member to define a cavity in the paving block. The side wallhas a bevelled edge which extends about a mouth of the cavity. At leastone protrusion extends along the second surface of the planar member.The protrusion may be a rib extending along a length of the secondsurface of the planar member.

The paving block is approximately 50% to 80% by weight crumb rubberwhich is less than 20 mesh crumb rubber, and approximately 18% to 40% byweight polyolefin having a melting index ranging from approximately 5g/10 minutes to approximately 50 g/10 minutes. The polyolefin isselected from the group consisting of polyethylene and polypropylene.The paving block may further include additives and colorants. Theadditives may include titanium dioxide, UV stabilizers, calciumcarbonate, talc and flame retardants.

There is also provided a method of manufacturing a paving block. Themethod comprises the steps of:

providing a mixture of approximately 50% to 80% by weight crumb rubberwhich is less than 20 mesh crumb rubber and 18% to 40% by weightpolyolefin having a melting index ranging between approximately 5 g/10minutes and approximately 50 g/10 minutes;

feeding the mixture of crumb rubber and granular polyolefin into abarrel and screw;

heating the mixture of crumb rubber and granular polyolefin in thebarrel to a temperature between 150° C. and 220° C.;

conveying the heated mixture of crumb rubber and granular polyolefinalong the barrel towards a nozzle; and

injecting the heated mixture through the nozzle into a mold.

Alternatively, the provided mixture may be approximately 55% to 75% byweight crumb rubber, approximately 23% to 48% by weight polyolefin, lessthan 10% additives and less than approximately 7% colorants. Stillalternatively, the provided mixture may be approximately 60% to 65% byweight crumb rubber, approximately 33% to 38% by weight polyolefin, lessthan 10% additives and less than approximately 7% colorants. Theadditives may include titanium dioxide, UV stabilizers, calciumcarbonate, talc and flame retardants.

The paving block disclosed herein has the advantage of being providedwith a bevelled edge to facilitate setting the paving block in theground. The paving block disclosed herein also has the advantage ofbeing provided with a hollow structure and protrusions which allow apaving block set in the ground to be anchored so as to restrict lateralmovement of the paving block. The paving block disclosed herein stillfurther has the advantage of being provided with a textured outersurface which reduces slippage and increases aesthetics.

The method of manufacturing the paving block disclosed herein providesthe advantage of reducing the burning and gassing of crumb rubber duringthe manufacturing process. Furthermore, because the paving block ispreferably manufactured from recycled rubber crumb and polyolefin, themethod of manufacturing the paving block disclosed herein isenvironmentally favourable.

BRIEF DESCRIPTIONS OF DRAWINGS

The invention will be more readily understood from the followingdescription of the embodiments thereof given, by way of example only,with reference to the accompanying drawings, in which:

FIG. 1 is a top isometric view of a first embodiment of an improvedpaving block formed in part from rubber crumb;

FIG. 2 is a bottom isometric view of the improved paving block of FIG.1;

FIG. 3 is a sectional view taken along line 3-3 of FIG. 1;

FIG. 4 is an front, sectional view of the paving block of FIG. 1illustrating the paving block being set in the ground;

FIG. 5 a top isometric view of a second embodiment of an improved pavingblock formed in part from rubber crumb;

FIG. 6 is a bottom isometric view of the improved paving block of FIG.5;

FIG. 7 a top isometric view of a third embodiment of an improved pavingblock formed in part from rubber crumb;

FIG. 8 is a bottom isometric view of the improved paving block of FIG.7;

FIG. 9 is a top isometric view of a plurality of improved paving blocksassembled to form a walkway; and

FIG. 10 is a simplified elevation view of an injection molding machineused to produce the improved paving blocks disclosed herein.

DESCRIPTIONS OF THE PREFERRED EMBODIMENTS

Referring to the drawings and first to FIGS. 1 and 2, these show animproved paving block 10. The paving block 10 includes a substantiallyplanar member 12 and a side wall 14 extending along a periphery of theplanar member. As best shown in FIG. 1, a first surface 16 of the planarmember 12 is an irregular textured surface and functions as a top of thepaving block 10. As best shown in FIG. 2, the side wall 14 extends alongand away from a periphery of the second surface 18 of the planar member12 to define a cavity 20 in the paving block 10. There is a bevel 22 onan inner side 23 of the side wall 14. This results in a bevelled edge 24extending about a mouth 26 of the cavity 20. There are a plurality ofprotrusions 28 a, 28 b and 28 c on the second surface 18 of the planarmember 12. In this example, the protrusions 28 a, 28 b and 28 c are inthe form of straight, parallel ribs extending along a length of thesecond surface 16 of the planar member 12. However, in other example theprotrusions may be curved or may be spikes.

Referring now to FIG. 3, the paving block 10 is formed from polyolefin30 and crumb rubber 32. The polyolefin 30 forms a matrix for an innerlayer of crumb rubber. Granules 34 and 36 of rubber crumb 32 may extendthrough the polyolefin 30. This provides the paving block 10 with atextured appearance and a non-slippery top surface. The paving block 10may also further include additional additives including colorants, flameretardants and UV stabilizers. In particular, titanium dioxide may beuseful for offsetting the black colour of the crumb rubber, allowing theblock to be coloured more vibrantly.

In operation, and as shown in FIG. 4, the paving block 10 is positionedat a desired position on the ground 40. This is shown in ghost in FIG.4. A downward force is then applied to planar member 12 of the pavingblock 10 in order to set the paving block in the ground 40. The bevellededge 24 of the paving block 10 facilitates insertion of the side wall 14into the ground 40. The cavity 20 of the paving block 10 is filled withground material as the paving block 10 is set into the ground. Thisallows the protrusions 28 a, 28 b and 28 c on the second surface 16 ofthe planar member 12 to function as anchors and restrict lateralmovement of the paving block 10. Although the paving block 10 shown inFIGS. 1 to 4 has an irregular shape, in other embodiments the pavingblock may have another shape.

FIGS. 5 and 6 show a square paving block 50. The paving block 50 issimilar to the paving block of FIGS. 1 to 4 in that the paving block 50has a bevel 52 on an inner side 53 of the side wall 51 which results ina bevelled edge 55. However, the paving block 50 of FIGS. 5 and 6 isfurther provided with intersecting ribs 54 a, 54 b and 54 c and aplurality of spikes 56 a, 56 b, 56 c and 56 d extending from the ribs.The spikes function as anchors and restrict lateral movement of thepaving block 50. The paving block 50 of FIGS. 5 and 6 is still furtherprovided with a plurality of gussets 58 a, 58 b and 58 c which functionto brace the side wall 51 of the paving block 50.

FIGS. 7 and 8 show a rectangular paving block 60. The paving block 60differs from the paving block of FIG. 1 to 4 in that the paving block 60has a bevel 62 on an outer side 63 of the side wall 61 which results ina bevelled edge 65. Ribs 64 a, 64 b and 64 c also extend along a widthof the paving block 60 as opposed to along a length of the paving block.As best shown in FIG. 7, the paving block 60 is also further providedwith chamfer 66 between the side wall 61 and a top surface 68 of thepaving 60.

The paving blocks disclosed herein may also be assembled in variety offormations to produce a variety of desired structures. For example, FIG.9 shows a plurality of the paving block 60 of FIGS. 7 and 8 assembled asa walkway.

The improved paving blocks disclosed herein are manufactured using aninjection molding machine 80 similar to the type shown in FIG. 10. Themachine 80 includes a feeder 82 in communication with a barrel 84. Ascrew 86 disposed within the barrel 84 is driven by a motor 88 andconveys a mixture of crumb rubber, polyolefin and any colorants oradditives along the barrel 84 while a heater 90 heats the mixture. Theheated mixture is injected into to a mold 92 and is formed into thepaving blocks disclosed herein.

A mixture of crumb rubber and granular polyolefin is heated in a barreland screw. The barrel is heated to a temperature between 150° C. and220° C. At this temperature the polyolefin will melt but the crumbrubber will not. The melted polyolefin forms a matrix about the crumbrubber as the screw shears rubber crumb and conveys the mixture towardsa nozzle which is in communication with a mold. The melted polyolefinand crumb rubber are injected into the mold. The mold is initially coldso the melted polyolefin solidifies about the crumb rubber to form apaving block. The polyolefin has melting index ranging betweenapproximately 5 g/10 minutes and approximately 50 g/10 minutes. Thepolyolefin is selected from the group consisting of polyethylene andpolypropylene. When the polyolefin is polyethylene the melting index isdetermined under the following conditions: 190° C. and 2.16 kg load.This corresponds to Condition E in ASTM test D1238. When the polyolefinis polypropylene the temperature is increased to 230° C.

The mixture may be approximately 50% to 80% by weight crumb rubber,approximately 18% to 40% by weight polyolefin, and approximately 2% byweight titanium dioxide. The crumb rubber is 10 mesh crumb rubber. Thepolyolefin had a melting index ranging between approximately 10 g/10minutes and approximately 30 g/10 minutes. Alternatively, the mixturemay be approximately 55% to 75% by weight crumb rubber, approximately23% to 48% by weight polyolefin, less than 10% additives, and less thanapproximately 7% colorants. Still alternatively, the mixture may beapproximately 60% to 65% by weight crumb rubber, approximately 33% to38% by weight polyolefin, less than 10% additives, and less thanapproximately 7% colorants. The additives may include titanium dioxide,UV stabilizers, calcium carbonate, talc and flame retardants.

Example 1

A paving block as disclosed herein was manufactured using a mixture of3762 grams of 9018—high density polyethylene from The Dow ChemicalCompany of Midland, Mich. (30% by weight) and 8778 grams of 10 meshcrumb rubber (70% by weight). The paving block was black in colour.

Example 2

A paving block as disclosed herein was manufactured using a mixture of3330 grams of 5270WZ polypropylene from Total Petrochemicals USA, Inc.of Houston, Tex. (37% by weight) and 5670 grams of 10 mesh crumb rubber(63% by weight). The paving block was black in colour.

Example 3

A paving block as disclosed herein was manufactured using a mixture of4257 grams of recycled polypropylene (33% by weight) and 8385 grams of10 mesh crumb rubber (65% by weight) and 258 grams of Black masterbatchof colour pigment pellets combined with a plastic resin carrier (2% byweight). The paving block was black in colour.

Example 4

A paving block as disclosed herein was manufactured using a mixture of4257 grams of recycled polypropylene (33% by weight), 8256 grams of 10mesh crumb rubber (64% by weight) and 387 grams of White masterbatch ofcolour pigment pellets combined with a plastic resin carrier (3% byweight). The paving block was light grey in colour.

Example 5

A paving block as disclosed herein was manufactured using a mixture of4257 grams of 4720—polypropylene from Total Petrochemicals USA, Inc. ofHouston, Tex. (33% by weight), 8127 grams of 10 mesh crumb rubber (63%by weight), 387 grams of Yellow masterbatch of colour pigment pelletscombined with a plastic resin carrier (3% by weight) and 129 grams ofWhite masterbatch of colour pigment pellets combined with a plasticresin carrier (1% by weight). The paving block was yellow green incolour.

Example 6

A paving block as disclosed herein was manufactured using a mixture of136 grams of 9018—high density polyethylene from The Dow ChemicalCompany of Midland, Mich. (34% by weight), 240 grams of 10 mesh crumbrubber (60% by weight) and 24 grams of Red masterbatch of colour pigmentpellets combined with a plastic resin carrier (6% by weight). The pavingblock was dark red in colour demonstrating that a whitening agent is notnecessary to color the paving block.

Example 7

A paving block as disclosed herein was manufactured using a mixture of4765 grams of 9018—high density polyethylene from The Dow ChemicalCompany of Midland, Mich. (38% by weight), 6270 grams of 10 mesh crumbrubber (50% by weight), 1254 grams of White masterbatch of colourpigment pellets combined with a plastic resin carrier (10% by weight)and 251 grams of Red masterbatch of colour pigment pellets combined witha plastic resin carrier (2% by weight). The paving block had a desertrose color and was both rigid and non-slippery. This demonstrates that50% by weight crumb rubber still provides sufficient rigidity.

It will be understood by a person skilled in the art that although thepaving block disclosed herein may be used in a variety of applicationsincluding but not limited to landscape paving, lawn edging, drivewayedging and decor.

It will further be understood by a person skilled in the art that themethod disclosed herein may be used to manufacture objects other thanpaving blocks, for example, artificial rocks and other articles.

It will be still further understood by a person skilled in the art thatmany of the details provided above are by way of example only, and arenot intended to limit the scope of the invention which is to bedetermined with reference to following claims.

1. A hollow paving block comprising: a substantially planar memberhaving a first surface and a second surface opposite the first surface,the first surface being a textured surface which functions as a top ofthe paving block; a side wall extending along and away from a peripheryof the second surface of the planar member to define a cavity in thepaving block, the cavity having a mouth, and the wall having a bevellededge extending about the mouth of the cavity; and at least oneprotrusion extending from the second surface of the planar memberwherein the paving block is formed from crumb rubber and a polyolefin,and the polyolefin forms a matrix for an inner layer of crumb rubberwith the textured surface being a result of granules of crumb rubberextending through the polyolefin matrix.
 2. The paving block as claimedin claim 1 wherein the said at least one protrusion is a rib extendingalong a length of the second surface of the planar member.
 3. The pavingblock as claimed in claim 1 the crumb rubber is less than 20 mesh crumbrubber.
 4. The paving block as claimed in claim 1 the crumb rubber is 10mesh crumb rubber.
 5. The paving block as claimed in claim 1 wherein thepolyolefin is selected from the group consisting of polyethylene andpolypropylene.
 6. The paving block as claimed in claim 1 wherein thepolyolefin has a melting index ranging between approximately 5 g/10minutes and approximately 50 g/10 minutes.
 7. The paving block asclaimed in claim 5 wherein the polyolefin has a melting index rangingbetween approximately 10 g/10 minutes and approximately 30 g/10 minutes.8. The paving block as claimed in claim 1 wherein the paving block isless than 50% by weight crumb rubber.
 9. The paving block as claimed inclaim 1 wherein the paving block is approximately 50% to 80% by weightcrumb rubber and approximately 18% to 40% by weight polyolefin.
 10. Thepaving block as claimed in claim 1 wherein the paving block isapproximately 55% to 75% by weight crumb rubber and approximately 23% to48% by weight polyolefin.
 11. The paving block as claimed in claim 1wherein the paving block is approximately 60% to 65% by weight crumbrubber and approximately 33% to 38% by weight polyolefin.
 12. The pavingblock as claimed in claim 1 wherein the paving block is also formed fromtitanium dioxide.
 13. The paving block as claimed in claim 12 whereinthe paving block is less than 2% by weight titanium dioxide.
 14. Ahollow paving block comprising: a substantially planar member having afirst surface and a second surface opposite the first surface, the firstsurface being a textured surface which functions as a top of the pavingblock; a side wall extending along and away from a periphery of thesecond surface of the planar member to define a cavity in the pavingblock, the cavity having a mouth, and the wall having a bevelled edgeextending about the mouth of the cavity; at least one protrusionextending along the second surface of the planar member, and wherein theblock is approximately 50% to 80% by weight crumb rubber which is lessthan 20 mesh crumb rubber, and approximately 18% to 40% by weightpolyolefin having a melting index ranging from approximately 5 g/10minutes to approximately 50 g/10 minutes and selected from the groupconsisting of polyethylene and polypropylene wherein the texturedsurface being a result of granules of crumb rubber extending through thepolyolefin matrix.
 15. The paving block as claimed in claim 14 whereinthe said at least one protrusion is a rib extending along a length ofthe second surface of the planar member.
 16. The paving block as claimedin claim 14 wherein the paving block is less than 2% by weight titaniumdioxide.
 17. The paving block as claimed in claim 14 wherein the crumbrubber has a particle size of 10 mesh or less.